A weather-resistant film for a front sheet of a solar cell and a method of manufacturing the same

Abstract

The application discloses a weather-resistant film for a front plate of a solar cell and a preparation method thereof, and the weather-resistant film is mainly composed of PVDF, wherein a plurality of sawtooth stripes with an isosceles triangle cross section are arranged on two side surfaces of the weather-resistant film in parallel at equal intervals, a protective layer is formed on the surface of the sawtooth stripe through vacuum sputtering, and the sawtooth stripes on the two side surfaces of the weather-resistant film are arranged perpendicularly to each other. The weather-resistant film has the sawtooth stripes arranged on the surface, so that the contact area with the adhesive can be increased, the overall adhesion of the weather-resistant film is increased, and the problem that the weather-resistant film is prone to delamination is avoided. In addition, the same sawtooth stripes are formed on the two side surfaces of the weather-resistant film, so that the manufacturing cost can be reduced, the sawtooth stripes with a certain size range can obtain better bonding performance on the inner side, and excellent dust adsorption resistance can be formed on the outer side.

Description

Technical Field

[0001] This application belongs to the field of solar cell technology, and in particular relates to a weather-resistant film for the front panel of a solar cell and its preparation method. Background Technology

[0002] Currently, widely used solar cells include crystalline silicon solar cells and thin-film solar cells. Flexible solar cells, a type of thin-film solar cell, are technologically advanced, have excellent performance, low cost, and wide applications. An important application area for flexible solar energy is building-integrated photovoltaics (BIPV), which can be integrated into windows or roofs, exterior walls or interior walls. To prevent damage and corrosion from moisture, ultraviolet radiation, and other environmental factors in practical applications, solar cells must be encapsulated and protected, forming a photovoltaic module. A photovoltaic module typically consists of a front panel, solar cells, encapsulation material, and a back panel. The solar cells are encapsulated between the front panel and the back panel using the encapsulation material.

[0003] Existing technologies typically use transparent fluoroplastic film as the outer weather-resistant film for the front panel. However, fluoroplastic films have high water permeability, poor abrasion resistance, low surface energy, and are prone to delamination and dust adsorption. After a period of outdoor use, conventional photovoltaic modules may still experience a decrease in power generation and delamination.

[0004] CN 108091715 A discloses a composite film for the front panel of a solar cell, including a support layer and a PVDF coating coated on the support layer, wherein the PVDF coating is sprayed onto the surface of the support layer as a weather-resistant layer.

[0005] CN 102019734 A discloses a protective film comprising a plastic film and a coating layer on the surface of the plastic film, wherein the coating layer comprises an adhesive and core-shell zinc oxide particles dispersed in the adhesive. This prior art improves light transmittance and weather resistance through the outer coating layer.

[0006] The weather-resistant coating on the front panel of the aforementioned prior art is too thin and located on the outermost side of the front panel, making it difficult to resist the erosion of wind and sand for a long time. Wind and sand dust can easily scratch the surface and reduce light transmittance.

[0007] CN 115179631 A discloses an encapsulation material comprising a fluoroplastic film and a water-blocking film, wherein the fluoroplastic film and the water-blocking film are connected by a weather-resistant pressure-sensitive adhesive layer, and a wear-resistant water-blocking layer is provided on the surface of the fluoroplastic film away from the water-blocking film; wherein the fluoroplastic film undergoes low-pressure low-temperature plasma surface treatment; the raw materials of the weather-resistant pressure-sensitive adhesive layer include acrylate pressure-sensitive adhesive, a combination of liquid ultraviolet absorbers, and a combination of solid ultraviolet absorbers. This prior art adds an extra water-blocking film to avoid water absorption and wear problems of the fluoroplastic film; however, the weather resistance of the water-blocking film is weaker than that of the fluoroplastic film, and the water-blocking film will become brittle and crack before the fluoroplastic film, thus failing to fundamentally solve the defects of the fluoroplastic film. Summary of the Invention

[0008] The technical problem to be solved by this application is to provide a weather-resistant film for the front panel of a solar cell and a method for preparing the same, so as to reduce or avoid the problems mentioned above.

[0009] To address the aforementioned technical problems, this application proposes a weather-resistant film for the front panel of a solar cell, which is mainly composed of PVDF. The weather-resistant film has multiple equally spaced parallel serrated stripes with cross-sections of isosceles triangles on both sides. A protective layer is formed on the surface of the serrated stripes by vacuum sputtering. The serrated stripes on both sides of the weather-resistant film are arranged perpendicularly to each other.

[0010] Preferably, the base of the isosceles triangle of the sawtooth stripe has a length of 5-10 μm, a vertex angle of 45-135 degrees, a height of 5-10 μm, and a minimum gap between adjacent sawtooth stripes of 0-5 μm.

[0011] Preferably, the maximum thickness of the weather-resistant film is 20-30 μm.

[0012] Preferably, the protective layer is made of silicon dioxide.

[0013] Preferably, the thickness of the protective layer is 1-3 μm.

[0014] Preferably, the angle between the length direction of the serrated stripes and the four rectangular sides of the weather-resistant film is 45 degrees.

[0015] This application also proposes a method for preparing a weather-resistant film for the front panel of a solar cell, comprising the following steps: providing a PVDF film mainly composed of PVDF; forming multiple equally spaced parallel serrated stripes with isosceles triangle cross sections on both sides of the PVDF film by hot pressing; and forming a protective layer on the serrated stripes by vacuum sputtering, thereby forming a weather-resistant film.

[0016] Preferably, the specific steps for forming the serrated stripes are as follows: using two rollers with patterns matching the shape of the serrated stripes placed vertically opposite each other, passing the heated PVDF film between the two rollers, and then air-cooling or water-cooling the PVDF film to obtain the cured serrated stripes on the PVDF film.

[0017] Preferably, the length directions of the patterns on the surfaces of the two rollers, which are positioned vertically opposite each other and match the shape of the sawtooth stripes, are perpendicular to each other.

[0018] Preferably, the pattern orientation on the surfaces of the two rollers forms a 45-degree angle with the direction in which the PVDF film is advanced.

[0019] The weather-resistant film of this application, through the serrated stripes on its surface, can increase the contact area with the adhesive, thereby increasing the overall adhesion of the weather-resistant film and avoiding the problem of easy delamination. In addition, forming the same serrated stripes on both sides of the weather-resistant film can not only reduce manufacturing costs, but also, by selecting a certain range of serrated stripes, better adhesion performance can be obtained on the inner side, and excellent dust resistance can be formed on the outer side. Attached Figure Description

[0020] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of this application.

[0021] Figure 1 The diagram shown is a structural schematic of a weather-resistant film for a solar cell front panel according to a specific embodiment of this application.

[0022] Figure 2 The diagram shown is a cross-sectional schematic of a weather-resistant film for a solar cell front panel according to another specific embodiment of this application.

[0023] Figure 3 The diagram shown is a structural schematic of a weather-resistant film for a solar cell front panel according to yet another specific embodiment of this application.

[0024] Figure 4 and Figure 5 They are displayed respectively Figure 3 The diagram shows the front and back sides of the weather-resistant film. Detailed Implementation

[0025] To provide a clearer understanding of the technical features, objectives, and effects of this application, specific embodiments are now described with reference to the accompanying drawings. Identical components are denoted by the same reference numerals.

[0026] As described in the background section, a typical solar photovoltaic (PV) module consists of a front panel, solar cells, encapsulation materials, and a backsheet. PV modules are typically used in outdoor environments, enduring wind, sun, rain, dust, and abrasion. Therefore, the performance requirements for the front panel, the light-receiving surface, are very high, requiring high light transmittance, water resistance, UV resistance, and a certain level of mechanical strength. The outermost layer of the front panel primarily serves to enhance performance, provide weather resistance, UV protection, moisture protection, low dielectric constant, and high breakdown voltage; this is generally referred to as the weathering layer. As mentioned earlier, some existing weathering layers use PVDF (polyvinylidene fluoride) coatings, while others use fluoroplastic films. The weathering layer is bonded to the supporting substrate of the front panel using adhesive.

[0027] The main component of a PVDF coating is the bonding resin, and the PVDF content is limited, resulting in inferior weather resistance compared to weather-resistant films with PVDF as the main component. However, PVDF weather-resistant films suffer from low surface energy and insufficient adhesion, making them prone to delamination. Additionally, their outer surface is not wear-resistant and easily attracts dust.

[0028] In view of this, this application proposes a weather-resistant film for the front panel of a solar cell, which is mainly composed of PVDF, wherein the mass content of PVDF in the weather-resistant film is greater than or equal to 90%, and ultraviolet light absorbers, wear-resistant fillers, etc. can be added to it to improve its performance.

[0029] Further, as shown in the figure, the weather-resistant film of this application is generally represented by reference numeral 1. Multiple equally spaced, parallel serrated stripes 11 with cross-sections of isosceles triangles are formed on both sides of the weather-resistant film 1. The serrated stripes on both sides of the weather-resistant film are identical. The dimensions of the weather-resistant film shown in the figure have been enlarged for easier observation and understanding. The actual size of the serrated stripes is relatively small, with only very subtle textures on the surface, which do not affect the overall light transmittance of the weather-resistant film. In one specific embodiment, the maximum thickness of the weather-resistant film is 20-30 μm.

[0030] Existing PVDF weather-resistant films suffer from low surface energy and insufficient adhesion, leading to a tendency to delaminate when bonded to a base film using adhesives. To overcome this problem, this application incorporates serrated stripes on the surface of the weather-resistant film. These stripes increase the contact area with the adhesive; for example, when the apex angle of the isosceles trapezoid of the serrated stripes is 60 degrees, the surface area is doubled, thereby increasing the overall adhesion of the weather-resistant film and preventing delamination.

[0031] It should be noted that improving the overall adhesion of the weather-resistant film actually only requires setting serrated stripes on the inner side of the film. However, since the stripes are very small and difficult to observe, the inventors chose to form the same serrated stripes on both sides of the weather-resistant film simultaneously for ease of assembly. This allows for film application on both sides, thus expanding the applicability of the weather-resistant film. The inventors believed that the serrated stripes on the outer side originally had no intended function. However, during actual installation experiments, it was found that if the size of the serrated stripes on the weather-resistant film surface is smaller than a certain range, they can act as a self-cleaning agent, reducing the adhesion of dust to the surface, and rainwater can easily wash away the attached dust. For example, in one specific embodiment, the isosceles triangle of the serrated stripe 11 preferably has a base length of 5-10 μm, a vertex angle of 45-135 degrees, a height of 5-10 μm, and a minimum gap between adjacent serrated stripes 11 of 0-5 μm. Forming identical serrated stripes on both sides of the weather-resistant film not only reduces manufacturing costs, but also allows for better adhesion on the inner side and excellent dust resistance on the outer side when selecting serrated stripes within this size range.

[0032] Furthermore, when identical sawtooth stripes are formed on both sides, these stripes may reflect sunlight, reducing the utilization rate of the solar cells. For example, once flexible solar cells are integrated onto a building, their orientation cannot be adjusted. When the sun's deflection angle is exactly perpendicular to one side of the sawtooth stripe surface, some light will be reflected back by that surface. While this can be avoided by adjusting the installation angle of the sawtooth stripes during installation, this requires very precise installation and is practically difficult to implement. To avoid the problem of reduced sunlight utilization due to improper installation angles on both sides, this application proposes a special design where the sawtooth stripes 11 on both sides of the weather-resistant film 1 are arranged perpendicularly to each other, thereby avoiding the problem of simultaneous reflection on both sides reducing sunlight utilization.

[0033] Furthermore, the serrated stripes on the surface of the weather-resistant film in this application can cause incident light to converge towards the center of the stripes, thus deflecting the angle of the light towards a direction as perpendicular as possible to the solar cell, thereby improving the utilization rate of sunlight in the tilted state. Regarding the principle of the serrated stripes converging light, the inventors drew inspiration from the prism film technology in the backlight panels of liquid crystal displays. Since the applicant's field happens to have many years of research and development in liquid crystal displays, the inventors were able to draw inspiration from the vastly different field of liquid crystal displays; however, such cross-disciplinary inspiration is not obvious to those skilled in the art of solar cells. Because the serrated stripes on both sides of the weather-resistant film are perpendicular to each other, they can play a certain role in correcting the direction of light from different directions, thus modulating the direction of light even under different solar altitude angles after installation.

[0034] Furthermore, to improve the adhesion of the weather-resistant film and prevent delamination, this application selects an angle of 45 degrees between the length direction of the serrated stripes and the four rectangular sides of the weather-resistant film. Figure 3-5 As shown. Generally, solar panels are designed in a rectangular shape with four perpendicular sides. If the length direction of the sawtooth stripes is perpendicular to one pair of rectangular sides of the weather-resistant film, then the other pair of rectangular sides will be parallel to the length direction of the sawtooth stripes. Since the stiffness of the sawtooth stripes differs in the length and width directions, their expansion rates also differ, which can cause the one pair of rectangular sides of the weather-resistant film to warp and delaminate. This application directs the direction of the sawtooth stripes at a 45-degree angle to the four rectangular sides. This makes the proportion of stiffness differences in different directions caused by the sawtooth stripes spreading to the four rectangular sides more even, thus avoiding the delamination problem of the weather-resistant film caused by the sawtooth stripes and further improving the structural performance of the weather-resistant film.

[0035] In order to improve the weather-resistant membrane's ability to resist wind and sand erosion, in another specific embodiment of this application, a protective layer 12 is formed on the surface of the sawtooth stripes 11 on the surface of the weather-resistant membrane 1 by vacuum sputtering. Preferably, the protective layer 12 is made of silicon dioxide and has a thickness of 1-3 μm.

[0036] The preparation method of the weather-resistant film for the front panel of a solar cell according to this application is further described in detail below with reference to the accompanying drawings. Specifically, the preparation method of this application includes the following steps:

[0037] First, a PVDF membrane mainly composed of PVDF is provided. This PVDF membrane can be a commercially available PVDF membrane with a thickness of 20-30μm, or it can be formed by melt co-extrusion and biaxial stretching of PVDF raw material particles with a mass content of ≥90%, with the addition of ultraviolet absorbers, wear-resistant fillers, etc.

[0038] Then, multiple equally spaced parallel serrated stripes 11 with isosceles triangular cross-sections are formed on both sides of the PVDF film by hot pressing. For example, two rollers with patterns matching the shape of the serrated stripes can be used, one above the other, to pass the heated PVDF film between the two rollers, and then the PVDF film is air-cooled or water-cooled to obtain the cured serrated stripes 11 on the PVDF film. The length directions of the patterns matching the shape of the serrated stripes on the surfaces of the two rollers are perpendicular to each other, thus forming mutually perpendicular serrated stripes 11 on both sides of the PVDF film. For example, if the pattern direction on the surfaces of the two rollers forms a 45-degree angle with the direction of the PVDF film's movement, serrated stripes 11 at a 45-degree angle to the four rectangular sides of the weather-resistant film can be formed.

[0039] Subsequently, a protective layer 12 is formed on the serrated stripes 11 by vacuum sputtering. For example, a silicon dioxide layer with a thickness of 1-3 μm can be formed on the serrated stripes 11 by vacuum sputtering. Since the thickness of the formed protective layer 12 is relatively very thin, Figure 2 The protective layer 12 is not shown in the text. Figure 1 The protective layer 12 in the image has also been enlarged for easier understanding.

[0040] Examples 1-6

[0041] The weather-resistant film for the front panel of a solar cell was prepared according to the parameters in the table below.

[0042]

[0043] In Examples 1-3, the angle between the serrated stripes and the rectangular side of the weather-resistant film is 45 degrees. In Examples 4-6, the angle between the serrated stripes and the rectangular side of the weather-resistant film is 0 / 90 degrees, that is, the angle between the serrated stripes and one pair of rectangular sides is 0 degrees, and the angle with the other pair of rectangular sides is 90 degrees.

[0044] Comparative Examples 1-6

[0045] Comparative Examples 1-6 used PVDF films without serrated stripes as weather-resistant films, with the following parameters.

[0046]

[0047] The weather-resistant films of Examples 1-6 and Comparative Examples 1-6 were respectively bonded to the surface of a 188μm PET support base film. The parameter performance of each example of the weather-resistant film was measured and compared as follows.

[0048]

[0049] As can be seen from the performance parameter comparison of the above embodiments, the weather-resistant film for the front panel of solar cells of this application can significantly improve the adhesion performance and avoid delamination when it has serrated stripes. At the same time, it can improve the light transmittance of oblique light, increase the contact angle of the outer surface, improve the self-cleaning ability, and have excellent dust adsorption resistance.

[0050] Those skilled in the art should understand that although this application is described by way of multiple embodiments, not every embodiment contains only one independent technical solution. This description is merely for clarity, and those skilled in the art should understand the specification as a whole and consider the technical solutions involved in each embodiment as being able to be combined with each other to form different embodiments to understand the scope of protection of this application.

[0051] The above description is merely an illustrative embodiment of this application and is not intended to limit the scope of this application. Any equivalent changes, modifications, and combinations made by those skilled in the art without departing from the concept and principles of this application shall fall within the scope of protection of this application.

Claims

1. A weather-resistant film for the front panel of a solar cell, mainly composed of PVDF, characterized in that, The weather-resistant film (1) has multiple equally spaced parallel sawtooth stripes (11) with an isosceles triangle cross section. A protective layer (12) is formed on the surface of the sawtooth stripes (11) by vacuum sputtering. The sawtooth stripes (11) on both sides of the weather-resistant film (1) are arranged perpendicular to each other. The angle between the length direction of the sawtooth stripes (11) and the four rectangular sides of the weather-resistant film (1) is 45 degrees.

2. The weather-resistant film as described in claim 1, characterized in that, The isosceles triangle of the sawtooth stripe (11) has a base length of 5-10 μm, a vertex angle of 45-135 degrees, a height of 5-10 μm, and a minimum gap between adjacent sawtooth stripes (11) of 0-5 μm.

3. The weather-resistant film as described in claim 1, characterized in that, The maximum thickness of the weather-resistant film is 20-30 μm.

4. The weather-resistant film as described in claim 1, characterized in that, The protective layer (12) is made of silicon dioxide.

5. The weather-resistant film as described in claim 1, characterized in that, The thickness of the protective layer (12) is 1-3 μm.

6. A method for preparing a weather-resistant film for the front panel of a solar cell, comprising the following steps: Provide a PVDF membrane mainly composed of PVDF; Multiple equally spaced parallel sawtooth stripes (11) with isosceles triangle cross sections are formed on both sides of the PVDF film by hot pressing; the length direction of the sawtooth stripes (11) forms an angle of 45 degrees with the four rectangular sides of the weather-resistant film (1); A protective layer (12) is formed on the serrated stripes (11) by vacuum sputtering, thereby forming a weather-resistant film (1).

7. The preparation method according to claim 6, characterized in that, The specific steps for forming the sawtooth stripes (11) are as follows: two rollers with patterns matching the shape of the sawtooth stripes (11) are placed opposite each other, and the heated PVDF film is passed between the two rollers. Then the PVDF film is cooled by air or water to obtain the cured sawtooth stripes (11) on the PVDF film.

8. The preparation method according to claim 7, characterized in that, The length directions of the patterns on the surfaces of the two rollers, which are positioned vertically opposite each other and match the shape of the serrated stripes, are set perpendicular to each other.

9. The preparation method according to claim 8, characterized in that, The pattern orientation on the surfaces of the two rollers forms a 45-degree angle with the direction in which the PVDF film is advanced.

Images